Sewing machine with upper feed

ABSTRACT

IN A SEWING MACHINE HAVING AN UPPER FEED DOG STRUCTURALLY COMBINED WITH THE PRESSER FOOT FOR BOTH HORIZONTAL AND VERTICAL OSCILLATING MOVEMENTS OF SAID DOG, AND A COMMON BIASING SPRING ARRANGED TO URGE BOTH THE PRESSER FOOT AND FEED DOG LIFT BARS INTO ENGAGEMENT OF THE PRESSER FOOT AND FEED DOG WITH THE WORK, AN AUXILIARY BIASING SPRING ACTING ON THE PRESSER FOOT BAR ONLY SERVES TO MAINTAIN THE SAME IN CONTINUOUS ENGAGEMENT WITH THE WORK, INDEPENDENTLY OF PRESSURE VARIATIONS ON THE WORK BY THE COMMON BIASING SPRING RESULTING FROM THE VERTICAL FEED DOG OSCILLATIONS.

Oct. 26, 1971 WENZ ETAL SEWING MACHINE WITH UPPER FEED Filed Aug. 21, 1968 INVENTORS fieegser ws/vz n HEM e a 8224 A'Aez. 424m ,4 rro eMEY United States Patent 61 hce 3,614,934 SEWING MACHINE WITH UPPER FEED Herbert Wenz and Heinrich Berg, Kaiserslautern, Pfalz,

Germany, assignors to G. M. Pfaff AG, Kaiserslautern,

Pfalz, Germany Filed Aug. 21, 1968, Ser. No. 754,223 Claims priority, application Germany, Sept. 28, 1967, P 30 14 752a Int. Cl. DOSb 27/04 US. Cl. 112-212 8 Claims ABSTRACT OF THE DISCLOSURE The present invention relates to upper work feed devices for sewing machines disposed above the stitching plate of the machine for the intermittent feeding of the sewing goods or workpiece singly or in combination with a conventional lower feed dog disposed below said plate.

The invention is more particularly concerned with upper feed devices of this type comprising a pair of lift bars, one for the work presser foot of conventional construction and the other for effecting the vertical oscillating movements of the feed dog operably connected to the presser foot lift bar. With suitable horizontal oscillating movements being imparted to said dog in proper relative phase and amplitude relation to its vertical oscillating movements, there result therefrom the usual fourmotion or quadrilateral feed movements for the intermittent advance of the work being operated on by a reciprocatory needle and looptaker, to form lock stitches in a manner well known.

Upper feed devices of the foregoing type advantageously utilize a common spring arranged to act directly on the lift bar of the feed dog, to normally urge said dog into engagement with the work upon the stitching plate, on the one hand, and said spring being furthermore arranged to act indirectly upon the presser foot lift bar via an oscillating operating lever pivoted to said bar and arranged to have one end periodically lift the feed dog lift bar against the action of said spring, to impart vertical oscillating movements to said dog. In other words, the common biasing spring for both the presser foot and feed dog lift bars acts to urge both the presser foot and feed dog into engagement with the work operated on.

Sewing machines having upper work feeding means of the afore-described type are subject to undesirable mechanical oscillations or vibrations of the feed dog lift bar, especially during relatively high sewing speeds, due to the recoil of the upper feed dog upon impinging upon the work or lower feed dog and due to the increasing inertial forces involved as the operating speed is increased. The result thereof is that the upper feed dog no longer engages the work both at the proper instant and with the requisite pressure, to ensure an accurate and proper advance of the work during a work feeding cycle or operation. Besides, the work presser foot is temporarily relieved, as a result of the recoil of the feed dog, of the action of the common biasing spring, lower- 3,614,934 Patented Oct. 26, 1971 ing or suspending thereby briefly the contact between the work and lower feed dog or work support (stitching plate), respectively, and resulting either in a complete interruption of the feed or in irregular feed movements and, in turn, uneven stitches being sewn by the machine.

Accordingly, an important object of the present invention is to overcome or minimize the above-mentioned and related difficulties and defects by ensuring at all times an adequate and constant operating pressure between the work and presser foot or stitching plate, respectively.

A more specific object of the invention is the provision of auxiliary biasing means in conjunction with an upper feed arrangement of the referred to type, ensuring a predetermined constant minimum pressure between the work and presser foot throughout a full work feeding cycle or operation.

The invention, both to the foregoing and ancillary objects as well as novel objects thereof, will be better understood by the following description, taken in conjunction with the accompanying drawing forming part Of this specification and in which:

FIG. 1 is a perspective view of an upper work feed arrangement for sewing machines embodying improved presser foot biasing means according to the invention; and

FIG. 2 is a fragmentary view of FIG. 1, showing a modification of the invention.

With the foregoing objects in view, the invention involves generally the provision, in an upper feed arrangement of the referred to type, of auxiliary biasing means for the presser foot to ensure, independently of the action and variations of the common biasing spring for both the presser foot and upper feed dog, a constant minimum pressure upon the work throughout the entire speed operating range of the sewing machine.

As a consequence, it is possible thereby to reduce the size of both the commond auxiliary biasing springs or equivalent resilient biasing means, thereby in turn reducing the danger of damage to the sewing goods.

Extensive tests made by applicant have shown that the use of an auxiliary biasing spring in an upper feed arrangement of the referred to type, embodying a common main biasing spring from both the presser foot and upper feed dog, will enable the operating speed of the machine to be increased considerably and safely, without involving any irregular feed movements or interruptions, or variations of the stitching length.

According to a first embodiment of the invention, to enable its use with varying work thickness, the auxiliary biasing spring takes the form of a coiled tension spring having one end secured to the presser foot bar and having its.other end secured to the frame of the machine via an adjustable set screw or the like, to enable and adaptation of the spring tension to the thickness of the work being operated on.

In the foregoing embodiment, with the tension of the auxiliary spring being applied laterally of the axis of the presser foot bar, canting and jamming of the pressure foot may occur. This can be avoided by the use of a flat auxiliary spring having a fork-shaped end symmetrically embracing the presser foot bar, in the manner as will become further apparent as the description proceeds in reference to the drawing.

Referring more particularly to FIG. 1, the numeral 1 denotes the main drive shaft of a conventional sewing machine driven in a known manner by an electric motor (not shown), said shaft carrying a first eccentric 2 embraced by one end of an eccentric bar 3. Rotati'vely mounted upon both sides of the opposite end of the eccentric bar 3 are a pair of slide blocks 4 and 5, respectively. Slide block 4 is arranged for movement within a grooved guide 6 the angular position of which is adjustable by means of a setting shaft 7, to control the work feed stroke and, in turn, the stitching length, in a manner as will become more apparent as the description proceeds.

Due to the positive guidance of the block 4 by the guide 6, the slide block 5, engaging a guide similar to the guide 6 and disposed at or integral with the end of a lever 8, acts to oscillate said lever being freely rotatively mounted, at its opposite end and via a sleeve 9, upon a rockshaft 10. The latter is in turn rotatively mounted in the frame of the sewing machine (not shown). The oscillations of the lever 8 are imparted, via a pivot 11 projecting from the guided end of the lever, at first upon a link 12 and from there, via a further pivot 13, upon one arm of a double-arm lever 14 rotatively supported about an axis 15 fixedly supported by the frame of the sewing machine.

The remaining fork-shaped arm of the lever 14 is connected, via a link 16, with the inner end 17 of an upper feed dog 18, whereby to oscillate the latter, via the eccentric 2, eccentric arm 3, lever 8, link 12, lever 14 and link 16, in a horizontal direction with a variable feed stroke determined by the angular setting of the stitch controller shaft 7.

The coordinate vertical oscillating movements of the feed dog 18 are derived from the drive shaft 1 via a second eccentric 19 having an eccentric bar 20 embracing the same, to transmit oscillating or rocking motion to the shaft 10 via a first crank 21 disposed at one end of said shaft.

Rockshaft 10 carries a second crank 22 at its opposite end which serves to transmit, by way of a link 23, the rotary motion of said shaft to an arm of an angular doublearm lever 24 rotatively mounted upon a pin 25 extending from an intermediate member 26 secured, such as by clamping, to the upper end of a presser foot lift bar 27. Further secured to the lower end of bar 27 is the presser foot proper 28 of usual construction, shown partly broken away in the drawing, and from the upper end of which extends a lateral arm 29 connected through a link 30 to the pivoted end 17 of the feed dog 18.

In the example shown, the fork-shaped outer end of the feed dog 18 embraces the work-engaging part of the presser foot 28 and cooperates with the lower feed dog 31, to intermittently feed the work being operated on. Alternatively, the work feed may be effected solely by the upper feed dog 18, while the presser foot may be of any suitable construction known, to engage the work or the stitching plate 32, respectively.

The angular lever 24 carries at its upper end a roller 33, said roller being arranged to engage or cam with, during rotation of the lever 24 by the link 23 towards its upper dead center position, with an intermediate mem her or cross-piece 34 secured to the upper end of a feed dog lift bar 35, thereby to lift said bar, normally urged in the downward direction by a flat spring 36 arranged with one end engaging the member 34 and having its opposite end secured to the frame of the machine. The feed dog lift bar 35, being disposed within and concentrically with the hollow presser foot bar 27, carries at its lower end a pin 37 embraced by a guide slot or fork 38 of the inner part of the feed dog 18, whereby to impart periodic vertical oscillating movements upon the feed dog about the pivot 17 by the vertical reciprocations of the feed dog lift bar 35.

The presser foot 28 serves in a known manner to urge the Work operated on against the lower feed dog 31, or stitching plate 32, respectively. Spring 36 is effectlve 1n exerting pressure on both the presser foot 28 via intermediate member 34, roller 33, lever 24, pivot pin 25, member 26 and presser foot bar 27, and on the feed dog 18 via lift bar and pin 37. In other words, the arrangement shown utilizes a common biasing spring 36 urging both the upper feed dog 18 and the presser foot 28 into engagement with the work being operated on.

In operation, in the lower dead center position of the roller 33, during the oscillations of the lever 24, in which the feed dog 18 is in engagement with the work, the lever 24 and in turn the presser foot bar 27 and presser foot 28 are temporarily relieved, to a certain extent, of the pressure of the spring 36, that is, the major portion of the pressure of the spring 36 acts upon the upper feed dog 18 which serves to feed or advance the work together or without the lower feed dog 31, in such a manner as to maintain a predetermined constant pressure upon the work or lower feed dog, respectively.

In the case of high sewing speeds, it may happen that the upper feed dog 18, together with its lift bar 35 and the intermediate member 34, is thrown abruptly in the upward direction against the action of the spring 36 as a result of the recoil effect at the instant of the feed dog 18 impinging upon the work overlying the lower feed dog 31 or stitching plate 32, respectively. As a consequence, the presser foot 28 is temporarily relieved of the effect of the spring 36, acting on both lift bars 27 and 35 in the manner described, whereby to become disengaged from the work with the result of an irregular feed movement, variations in stitching length and other drawbacks and defects resulting therefrom.

In order to overcome the foregoing difiiculty, or to ensure the work to be in continuous engagement with the pressure foot 28, on the one hand, and with the feed dog 31 or stitching plate 32, on the other hand, independently of the recoil effects mentioned during relatively high sewing speeds, there is provided in accordance with the improvement of the present invention an auxiliary biasing spring or equivalent resilient means acting upon the presser foot independently of the common biasing spring 36 described hereinbefore. The auxiliary biasing spring may be constructed in any suitable manner, such as in the form of a coiled tension spring 39 as shown in FIG. 1, or as a flat spring 40 as shown in FIG. 2, the spring tension being advantageously adjustable, to adapt the same to a varying work thickness, or other characteristics of the work being operated on.

More particularly, according to the FIG. 1 modification, one end of the spring is held by or secured to a pin 41 extending from the intermediate member 26 fast upon the presser foot bar 27, while the opposite end of the spring 39 is secured to an outwardly threaded head pin 42 mounted in the stepped bore 43 of a threaded bush 44 secured in the frame of the machine. Pin 42 constituting a set screw cooperating with the bush 44 enables an adjustment of the tension of the spring 39, for adapting the device to sewing goods of varying thickness and/ or other characteristics.

According to the FIG. 2 modification of the invention, the auxiliary flat spring 40 embraces with its forkshaped inner end 45 the presser foot lift bar 27 in engagement with the upper face of the intermediate member 26 fast on said bar. The pressure of the spring 40, having its opposite end (not shown) secured to the frame of the machine, upon the presser foot 28 is adjusted in this case by means of a set screw 46, or in other suitable manner.

While the auxiliary biasing spring 39, FIG. 1, and 40, FIG. 2, primarily serves to avoid the defects described resulting from the feed dog recoil action upon the work during high operating speeds, it provides the additional advantage that the size of the Common biasing spring 36 may be reduced as a result of the continuous action of the springs 39 or 40 on the presser foot 28 in the manner described herein.

In the foregoing the invention has been described in reference to a specific illustrative or exemplary device. It will be evident, however, that variations and modifications as well as the substitution of equivalent parts or elements for those shown herein for illustration, may be made without departing from the broader scope and spirit of the invention as set forth in the appended claims. The specification and drawing are to be regarded, therefore, in an illustrative rather than in a restrictive sense.

We claim:

1. Ina sewing machine,

(1) a drive shaft,

(2) a stitching plate,

(3) a work presser foot,

(4) a presser foot lift bar,

(5) a four-motion upper feed dog,

(6) first motion transmitting and converting means operably connecting said shaft with said feed dog, to impart horizontal oscillating component motion to said dog,

(7) a feed dog lift bar,

(8) first resilient biasing means effective upon said feed dog lift bar, to urge said feed dog into engage ment with said said stitching plate,

(9) second motion-transmitting and converting means operably connecting said shaft with said feed dog lift bar and including a double-armed operating lever pivoted to said presser foot lift bar and having a lever arm engaging said feed dog lift bar, to urge said presser foot into engagement with said plate by said biasing means and to impart vertical oscillating component movement to said dog, and

(10) second resilient biasing means effective upon said presser foot lift bar, to urge said presser foot into constant pressure engagement with said plate, substantially independently of said first biasing means.

2. In a sewing machine as claimed in claim 1, including means to adjust the pressure applied by said second resilient biasing means to the work via said presser foot.

3. In a sewing machine as claimed in claim 1, said second resilient biasing means consisting of a coiled tension spring having one end secured to said presser foot lift bar and having its opposite end secured to the frame of the machine, and means to adjust the tension of said spring.

4. In a sewing machine as claimed in claim 1, said first biasing means consisting of a fiat spring arranged with one end engaging a cross-piece upon the upper end of said feed dog lift bar and said lever arm carrying a roller engaging the undersurface of said crosspiece.

5. In a sewing machine as claimed in claim 1, said second resilient means consisting of a flat spring having a fork-shaped end embracing said presser foot lift bar and resting against a collar-like extension of said bar, and means to adjust the pressure of said spring upon said extension.

6. In a sewing machine as claimed in claim 1, said feed dog lift bar being mounted within and concentrically with said presser foot lift bar.

7. In a sewing machine as claimed in claim 1, including means to adjust the constant pressure on the work by said second resilient biasing means.

8. In a sewing machine as claimed in claim 1, including a link construction between said feed dog and said presser foot lift bar.

References Cited UNITED STATES PATENTS 376,122 1/1888 Tucker 112--207 2,339,240 1/ 1944 Clayton 112-207 3,009,432 11/1961 Reeber et al. 1l2-212 RICHARD J. SCANLAN, JR., Primary Examiner 

